This invention relates to reversible heat pump systems which condition water that is to be circulated through one or more heat exchangers downstream of the heat pump system.
Heat pump systems which provide heated or cooled water to one or more heat exchangers are typically not required to switch from a heating mode to a cooling mode very often. This is in part due to the inherent inertia of a heat pump in trying to heat water that has been previously cooled. In this regard, the compressor within the heat pump must process a sufficient amount of refrigerant over time that can give up the necessary heat to the water that has been previously cooled. The compressor is presented with a similar heavy load situation when it is required to process a sufficient amount of refrigerant over time to absorb heat from previously heated water so as to produce cooled water. This inability to switch between heating and cooling or vice versa has previously led to switching the mode of operation of the heat pump system infrequently. For instance, changeovers would be implemented on particular calendar dates indicating normal change of seasonal weather conditions. On the other hand, a changeover might be implemented depending on a separately sensed outdoor air temperature indicating whether the heat pump system should be in either heating or cooling for the day. The above described changeover controls do not allow a heat pump system to respond to heating or cooling demands that may change throughout the day. The above described systems moreover do not respond to different demands for cooling or heating throughout a building on a given day.